A method of inducing and isolating genetic variants affecting senescence is described. Mutations are induced chemically or by radiation in chromosomes of sperm. Treated males are mated to attached-X females and the F1 males allowed to age. At appropriate times of their adult lifespan, F1 males are tested for behavioral modifications atypical for their ago. The documented correlation between progressive retardation of geotactic and mating reactions and degenerative changes in the central nervous system of aging males strongly suggests that if mutants significantly altering the rate of senescence can be generated, they will be detected. The basic technique and its modifications should efficiently select for many possible types of mutation which will be characterized both genetically and with regard to general mode of action. Organ transplantation experiments will be carried out during the search for mutants. Polytene chromosomes of aging flies will be studied for age-correlated changes in gene activity. These studies have the aim of determining the relative contributions of genes, of factors in the hemolymph and of various organs to the process of aging in Drosophila.